Question: Reduce to simplest form. $-\dfrac{9}{12}-\left(-\dfrac{7}{4}\right)=$
$=-{\dfrac{9}{12}} +{\dfrac{7 \cdot 3 }{4 \cdot 3}}$ $=-{\dfrac{9}{12}}+{\dfrac{21}{12}}$ $=\dfrac{12}{12}$ $=1$